This invention relates generally to planar-type loudspeakers having a substantially flat diaphragm.
In recent years, certain advances in dynamic loudspeaker design have been provided by the advent of planar diaphragm loudspeakers. Such loudspeakers include a relatively stiff and substantially planar (or flat) diaphragm that is mounted in a frame and that is coupled at its rear surface to a speaker voice coil, such that the voice coil acts like a piston, pressing on the rear surface of the diaphragm and causing sufficient vibration of the diaphragm to efficiently produce sound. Examples of such planar diaphragms are shown and described in U.S. Pat. Nos. 4,003,449 and 4,997,058, both issued in the name of Jose J. Bertagni.
Typically, a planar diaphragm is constructed of a pre-expanded cellular plastic material, such as polystyrene or styrofoam. The advantages provided by planar diaphragm loudspeakers over loudspeakers utilizing conventional cone-type diaphragms include greater dispersion of sound and economy of manufacture. Moreover, the front surface of a planar diaphragm can be molded to take on the appearance of a relatively large acoustic tile, permitting unobtrusive installation of the loudspeaker in ceilings of commercial structures formed of like-appearing acoustic tiles. Alternatively, the diaphragm's front surface can be molded smooth and flat for installation as a seamless part of a plasterboard wall or ceiling, as shown and described in co-pending application Ser. No. 07/866,067, entitled Planar-type Loudspeaker With Dual Density Diaphragm, filed Apr. 9, 1992 in the name of Alejandro J. Bertagni et al., and assigned to the same assignee as the present application. A number of such diaphragms also can be joined together in a contiguous and seamless array to create a sound screen upon which video images can be projected, as shown and described in U.S. Pat. No. 5,007,707, issued in the name of Jose J. Bertagni.
Ideally, a loudspeaker exhibits a substantially flat or level response characteristic over the frequency range of sounds that it is designed to reproduce. The frequency response of a planar diaphragm generally is determined by the type and density of its material, and the area, thickness and contour of its sound producing region. Weights also may be inserted in recesses formed in the rear surface of the diaphragm in order to balance it and help shape its frequency response characteristic. These weights are adhered in place by an epoxy cement which drys to a relatively hard state and holds the weights fixedly in place within the recesses.
Balancing weights have been useful in reducing the excursions (i.e., peaks and valleys) in the frequency response of planar diaphragms from a flat or level characteristic. The effectiveness of these weights, however, has proven to be limited. Accordingly, the resulting frequency response characteristic has not always been as flat or level as desired.
Thus, it will be appreciated that there exists a need for improvement in planar diaphragm loudspeakers to provide a better frequency response characteristic. The present invention fulfills this need.